Welcome to B&B!
My first thought was that maybe you might be using incrementally more pressure on one side of your face than the other... the second thought was that maybe you've been using a different razor lately, but when you say you have not done anything different, that might include not changing your razor over the past month.
How many passes do you do, usually? Is this "burnt spot" one of your normal touch-up areas? Do you blade-buff?
(lots of questions, admittedly)
On the wrist this week: Fortis Millenium Starship Limited Edition Flieger Chrono in Valjoux 7750